Typical telephone networks that are used conventionally to connect residential and business telephone lines form a public switched telephone network (“PSTN”) which encompasses most of the world's collection of voice-oriented public telephone networks. The PSTN is an aggregation of circuit switching telephone networks which route phone calls between consumers. Today, the PSTN includes almost entirely digital technology, but some analog remnants remain (e.g., the final link from a central office to the user). The transmission and routing of calls via the PSTN is governed by a set of standards, so that various providers of telephone service may easily route calls between their customers. Thus, a first consumer having telephone service A is able to call a second consumer having telephone service B, and the routing of such a call may go through networks owned by various other telephone services C-E. The result is the appearance of a seamless transmission between the first and second consumer.
As an alternative to using standard telephones on the PSTN, consumers may also use their personal computers (“PCs”) to make phone calls to other PC users. The transmission of a call via a PC is generally referred to as Voice over Internet Protocol (“VoIP”) technology. VoIP is a set of facilities for managing the delivery of voice information using the Internet Protocol. These PC to PC phone calls are transmitted via the Internet. However, in some instances, a consumer on a standard telephone may desire to call a consumer using a PC phone, or vice versa. Thus, standards have been developed to effectively route these types of phone calls between the PSTN and VoIP networks.
A variety of protocols are used to handle telephone calls made to and from PC's, such as the MEGACO standard by the Internet Engineering Task Force (IETF), the Media Gateway Control Protocol (MGCP) and the Session Initiation Protocol (SIP). These protocols seek to bridge the gap between circuit based public switched networks and Internet Protocol (IP) based networks. Each of the protocols uses different conventions and has different sets of function calls and variables, which generally require an interface tailor made for the specific protocol to communicate with the transport layer. On the other hand, many different protocols also exist at the transport layer level, where the calls are routed to the Internet. The User Datagram Protocol (UDP), Stream Control Transmission Protocol (SCTP) and the Transmission Control Protocol (TCP) are three such protocols. Access to these protocols also requires an interface that is specific to that protocol.
Media Gateway units (MG's) are the elements that physically connect the computer network elements of the telephone system with the conventional telephone network elements (PSTN), to provide the VoIP capability. The primary function of the MG unit is to provide hardware services, and thus typically it may include codecs, compression devices (DSP's), tone generation and detection functions, line terminations such as T1, ISDN, POTS and ATM VC's, etc. The media gateway unit generally includes two principal components. One component is the user's application that is implemented on the MG, and is referred to as the hardware service provider (HSP). Another component is the media gateway software component, which carries out media gateway functions not implemented in the HSP, such as interfacing with the network protocols.